The Effect of Geometric Scaling on Aerodynamic Performance

Miniaturization of modern electronics and simultaneous elevation in heat dissipation means that future compact electronic systems are likely to be too hot to be held in the users hand. As a result, novel compact cooling technologies are required. In systems such as mobile phones and palmtop computers, macroscale fans cannot be used to overcome this problem because they are too large. As a solution, the implementation of microfan technology is proposed. Aerodynamic scaling issues in microaxial flow fans are addressed. Analysis shows how reduction of fan dimensions to the microscale causes increased local loss. Numerical simulations were performed to investigate the validity of the scaling theory, the results of which give confidence in the scaling analysis. Measurements were carried out on two geometrically similar fans to validate the theory under experimental conditions. Results of these measurements were in good agreement with the analysis. The fundamental finding is that a reduction in scale is accompanied by a reduction in efficiency and, thus, fan performance. It is concluded that geometric scaling alone of macroscale designs is not sufficient to produce microscale cooling fans: Modifications must be made to the geometry that account for changes in flow physics.